A very high percentage (>90%) of prostatic cancers show common chromosomal losses or deletions (i.e., Ch. 10q24; 5q13; and 16q), indicating the involvement of putative suppressor genes in the tumors. In view of this, we have isolated and are in the process of characterizing cDNA clones obtained by utilizing a novel subtractive hybridization method developed at LMO using three different human prostatic cell lines (LnCaP, DU-145 and PC-3) that contain deletions in Ch. 10 or other loci. LnCaP exhibits a typical 10q24 deletion, is well differentiated and hormone responsive; DU-145 is moderately differentiated; the PC-3 cell line has complex chromosomal rearrangements and is completely undifferentiated. In this way, we have discovered a novel DNA binding protein showing many similarities with the HRNP A1, UP1 group of proteins, most probably involved in the regulation of transcription and/or translation, both activities related to cell growth. This novel gene seems to be overexpressed in prostate tumors but not in normal prostate tissue. Further studies of differential expression pattern of this cDNA clone and the protein it encodes, between early stage tumor tissues (A, B) and late stage samples (C, D), are in progress. We also looked for differentially expressed cDNAs by the means of differential display technique using the RNAs of the same prostate tumor cell lines. By this method, we have isolated and characterized a number of clones, among which some of them are unique and need further characterization.